There is a significant need for a liquid pavement marking composition that will provide increased durability and retained reflectivity once applied to a surface and dried or cured. Compositions of this type are typically used on roads, highways, parking lots, and recreational trails, to form stripes, bars and markings for the delineation of lanes, crosswalks, parking spaces, symbols, legends, and the like. They are typically applied by spray coating (i.e., painting) the pavement surface. Preformed pavement marking sheets or tapes have also been used to mark pavement or traffic bearing surfaces.
Pavement marking stripes, or pavement markings of other shapes, may include reflective optical elements adhered to the pavement surface by the use of a binder. Current traffic paint systems typically use conventional 1.5 nD glass microspheres for retroreflection. The microspheres are typically flood coated onto the wet marking immediately after coating. This provides the paint with improved retroreflectivity and also covers the top surface of the uncured or undried coating with a protective layer of microspheres. This protective layer allows the markings to be exposed to traffic sooner because of the layer of microspheres over the surface, which prevents transfer of the coating to the surface of vehicle tires. This is important for rates of marking application. The time between application and the point where material will no longer transfer to vehicle tires is defined as the xe2x80x9ctrack-freexe2x80x9d time. Shorter track-free times increase marking efficiency by reducing or eliminating the need for traffic disruption through such measures as closing lanes or placing traffic control devices to protect such markings.
It would be advantageous to apply markings in a wider range of weather conditions than is possible with existing compositions. There is also a need for marking compositions with improved cure profiles to ensure both substrate wet out and rapid track-free time. Furthermore, improvements are needed to obtain compositions that are substantially free of volatile organic components.
The present invention provides a pavement marking including a binder having polyurea groups. Conventional liquid pavement marking compositions include alkyd-based binder compositions as described in U.S. Pat. Nos. 2,897,732 (Shuger), 2,897,733 (Shuger), and 3,326,098 (Boettler), and epoxy-based compositions as described in U.S. Pat. Nos. 4,088,633 (Gurney), 4,185,132 (Gurney), and 4,255,468 (Olson). Such conventional compositions are not desirable for at least one of the following reasons: they typically dry too slowly; they need elevated temperatures for reasonable cure times; they contain chemical linkages (e.g., ester linkages) that are susceptible to degradation (as by hydrolysis, for example); and/or they require the use of organic solvents, drying oils, or drying accelerators, which can lead to discoloration.
Numerous other conventional pavement marking compositions have been developed to get faster dry times by using heated application of materials to road surfaces. Also, waterborne coatings based on acrylic latices, as disclosed in U.S. Pat. No. 5,527,853 (Landy et al.), and epoxy resin emulsions, as disclosed in U.S. Pat. No. 4,906,716 (Cummings), have been suggested for use in pavement markings. Such markings do have the advantages of low volatile organic content and one part coating compositions, but they are not yet sufficiently durable for long term road presence and retained reflectivity performance.
U.S. Pat. No. 4,076,671 (Bright) discloses a resinous composition said to be useful for marking trafficable surfaces. The two part acrylate based coating compositions are said to provide a desirable balance of stability and fast cure, but require the use of free monomers and low molecular weight ethylenically unsaturated compounds which have significant vapor pressures. Also, they require the use of peroxide catalysts. U.S. Pat. No. 5,478,596 (Gurney) discloses liquid pavement marking compositions prepared from a two part polyurethane-forming system of a first component having isocyanate-reactive groups (a polyol) and a second component having isocyanate groups.
A need exists for liquid pavement marking compositions that can provide one or more, and preferably all, of the following features: reduced environmental impact through formulations having low volatile organic content; improved balance of coating rheology during application and film formation to promote substrate wet out and fast cure to track-free films; broadened range of weather conditions for coating application; and/or improved marking performance through increased durability and retained reflectivity. To achieve one or more, and preferably all, of these features, the present invention provides a pavement marking including a binder having polyurea groups.
Pavement markings of the present invention preferably include a binder having polyurea groups, wherein the binder is prepared from a coating composition comprising one or more aliphatic secondary amines, one or more polyisocyanates, material selected from the group of fillers, extenders, pigments, and combinations thereof, and reflective elements (e.g., glass beads, etc.). Preferably, the pavement marking has a retained reflectivity of at least about 100 mcd/m2/lux after at least about 2 years in use as longitudinal traffic markings as measured according to ASTM E 1710-95. Preferably, the binder is prepared from a two-part coating composition comprising an amine component comprising one or more aspartic ester amines and optionally one or more amine-functional coreactants, and an isocyanate component comprising one or more polyisocyanates. A traffic bearing surface having thereon such a pavement marking is also provided.
Also provided is a pavement marking that includes a binder having polyurea groups, wherein the binder is prepared from a sprayable, two-part coating composition substantially free of volatile organic components and comprising an amine component comprising one or more aspartic ester amines and an isocyanate component comprising one or more polyisocyanates. At least one of the amine component and/or the isocyanate component further comprises material selected from the group of fillers, extenders, pigments, and combinations thereof. The coating composition has a minimum application temperature of at least about 7xc2x0 C. and a track-free time of no greater than about 5 minutes. A traffic bearing surface having thereon such a pavement marking, and a pre-formed pavement marking wherein the pavement marking is coated on a substrate that can be applied to a traffic bearing surface are also provided.
The present invention also provides coating compositions. In one embodiment, the coating composition includes one or more aliphatic secondary amines, one or more polyisocyanates, and material selected from the group of fillers, extenders, pigments, and combinations thereof. The coating composition has a minimum application temperature of at least about 7xc2x0 C., a track-free time of no greater than about 5 minutes, and forms a pavement marking having reflective elements with a retained reflectivity of at least about 100 mcd/m2/lux after at least about 2 years in use as longitudinal traffic markings as measured according to ASTM E 1710-95.
Also provided is a sprayable two-part liquid pavement marking composition comprising an amine component comprising one or more aspartic ester amines and optionally one or more amine-functional coreactants, and an isocyanate component comprising one or more polyisocyanates. The amine component, the isocyanate component, or both further comprise material selected from the group of fillers, extenders, pigments, and combinations thereof. The coating composition is sprayable and has a minimum application temperature of at least about 7xc2x0 C. and a track-free time of no greater than about 5 minutes. Preferably, the pavement marking composition comprises an amine component comprising one or more aspartic ester amines and optionally one or more amine-functional coreactants, and an isocyanate component comprising one or more polyisocyanates.
Methods of applying such compositions are also provided. For example, a method of marking a traffic bearing surface is provided. This method includes providing an amine component comprising one or more aspartic ester amines and optionally one or more amine-functional coreactants, providing an isocyanate component comprising one or more polyisocyanates, providing material selected from the group of fillers, extenders, pigments, and combinations thereof in either the amine component, the isocyanate component, or both, combining the amine component and the isocyanate component to form a coating composition having a minimum application temperature of at least about 7xc2x0 C., and a track-free time of no greater than about 5 minutes, spraying the coating composition onto a traffic bearing surface, and applying reflective elements to the composition coated on the traffic bearing surface to form a pavement marking.
Another embodiment includes a method of preparing a pavement marking. This method includes providing an amine component comprising one or more aliphatic secondary amines, providing an isocyanate component comprising one or more polyisocyanates, providing material selected from the group of fillers, extenders, pigments, and combinations thereof in either the amine component, the isocyanate component, or both, combining the amine component and the isocyanate component to form a coating composition having a minimum application temperature of at least about 7xc2x0 C., and a track-free time of no greater than about 5 minutes, applying the coating composition to a surface, and applying reflective elements to the composition coated on the surface to form a pavement marking having reflective elements with a retained reflectivity of at least about 100 mcd/m2/lux after at least about 2 years.